X-raying the Mach cones of Virgo Cluster spiral galaxies
Matthias Ehle XMM-Newton Science Operations Centre, European Space Astronomy Centre, ESA, Madrid
M. Weżgowiec, B. Vollmer, R.-J. Dettmar, D. J. Bomans, K. T. Chyży, M. Urbanik and M. Soida X-raying the Mach cones of Virgo Cluster spiral galaxies
Menu of the Day:
The Frame Work: Galaxy Evolution by Interactions Our Laboratory: Galaxies in the Virgo Cluster Numerical Models Expectations: Mach cones Method, targets and observational results: 3 spiral galaxies Conclusions
Structure in Clusters and Groups of Galaxies in the Chandra Era | X-raying the Mach cones of Virgo Cluster spiral galaxies | M. Ehle | Pag. 2 The Frame Work: Galaxy Evolution by Interactions
Interaction of a spiral galaxy with its environment
Gravitational interaction galaxy - cluster
Gravitational interaction galaxy - galaxy (Böhringer et al. 1994)
(Kenney et al. 1995)
Ram pressure galaxy ISM – intracluster medium (ICM)
(Kenney et al. 2004)
Structure in Clusters and Groups of Galaxies in the Chandra Era | X-raying the Mach cones of Virgo Cluster spiral galaxies | M. Ehle | Pag. 3 The Frame Work: Galaxy Evolution by Interactions
Interaction Diagnostics
Which interaction is responsible for the observed distortions/perturbations?
Determination of the interaction parameters
Determination of evolutionary path of a galaxy in a cluster
Means: HI maps and velocity fields, dynamical simulations, polarized radio continuum emission, soft diffuse X-ray emission
Structure in Clusters and Groups of Galaxies in the Chandra Era | X-raying the Mach cones of Virgo Cluster spiral galaxies | M. Ehle | Pag. 4 Our Laboratory: Galaxies in the Virgo Cluster
Radially truncated gas
4321=M100 disks (Cayatte et al. 1990, Chang et al. 2009) 4501=M88 4254=M99 4302/4298 4548=M91
4569=M90 4438 M86/M84 Long HI tails (Chung et al. M87 4388 2007)
4535 Asymmetric polarized radio ridges marking gas M49 compressions and shear motions (Weżgowiec et al. VIVA 2007, Vollmer et al. 2007) VLA Imaging of Virgo in Atomic Gas
(A. Chung, J. van Gorkom, J. Kenney, H. Crowl, B. Vollmer)
Structure in Clusters and Groups of Galaxies in the Chandra Era | X-raying the Mach cones of Virgo Cluster spiral galaxies | M. Ehle | Pag. 5 Numerical Models
Model-based time sequence for ram pressure stripping in the Virgo cluster (Vollmer 2009)
• Snapshots of 3D models including ram pressure compared to observed HI gas distribution & velocity fields • 3D velocity vectors and time steps are matched with observed projected position and radial velocity of the galaxy
pre-peak near peak ~150 Myr after peak ~300 Myr after peak
Structure in Clusters and Groups of Galaxies in the Chandra Era | X-raying the Mach cones of Virgo Cluster spiral galaxies | M. Ehle | Pag. 6 Observing Interactions: The X-ray Method
Soft diffuse X-ray emission – a rather new diagnostic tool for interactions
Diffuse X-ray emission traces distribution of very hot gas from the ISM and ICM:
~ flux ne nH In addition, spectral analysis allows us to derive temperatures, i.e. trace outflow, and study the interface and mixing at the ISM/ICM border
Expectations: Hot gas might be expelled, stripped or trailing Ram pressure stripping heats gas to X-ray temperatures (shocks, heat conduction, mixing of stripped ISM with intracluster medium) (Stevens et al. 1999, Roediger et al. 2006) Supersonic velocities of cluster galaxies cause bow shocks with associated Mach cones
Structure in Clusters and Groups of Galaxies in the Chandra Era | X-raying the Mach cones of Virgo Cluster spiral galaxies | M. Ehle | Pag. 7 Method, targets and observational results
Search for Hot Gas in Mach cones around Virgo Cluster spiral galaxies:
Detailed comparison between observations and simulations of ram pressure stripped spiral galaxies in the Virgo cluster Can derived Mach cone geometries be seen in hot gas? Look at low resolution maps of diffuse extended X-ray emission Study X-ray spectra to derive gas temperatures for comparison with ICM
Done, with XMM-Newton, for 3 galaxies: NGC 4501, NGC 4388 and NGC 4569…
(full details in our recent paper: Weżgowiec et al. A&A 531, 44, 2011)
Structure in Clusters and Groups of Galaxies in the Chandra Era | X-raying the Mach cones of Virgo Cluster spiral galaxies | M. Ehle | Pag. 8 Observational results (1/4)
NGC 4501: Strong compression of B-field in the SW (Weżgowiec et al. 2007, Vollmer et al. 2007) Sharply truncated HI disk
In X-rays: Moderately extended hot gas halo Hot gas tail at ~ 0.7 keV
Conclusions: Distribution fits ram pressure stripping model Extra-planar X-rays due to stripped gas mixed with intracluster medium and/or galactic wind from SF?
Structure in Clusters and Groups of Galaxies in the Chandra Era | X-raying the Mach cones of Virgo Cluster spiral galaxies | M. Ehle | Pag. 9 Observational results (2/4)
NGC 4388: Impressive hot gas tail associated with Hα plume (Yoshida et al. 2002) Huge HI tail discovered by Oosterloo & van Gorkom (2005)
In X-rays: Map cut where contributions from M86 halo start to dominate Spectrum of hot gas tail: two temp MEKAL: hot ISM (~0.9 keV) plus ICM (~2.3 keV)
Conclusions: Thermal pressure in tail a few times lower than estimated ram pressure 8 Estimates total gas mass of tail (~6x10 Msun) 9 << stripped gas mass; HI deficiency (2x10 Msun) Strong ISM-ICM mixing & initial stripping of outer gas disk (Vollmer & Huchtmeier, 2007)
Structure in Clusters and Groups of Galaxies in the Chandra Era | X-raying the Mach cones of Virgo Cluster spiral galaxies | M. Ehle | Pag. 10 Observational results (3/4)
NGC 4569: One of the largest & most HI deficient galaxies (Solares et al. 2001) Large radio lobes (Chyży et al. 2006)
In X-rays: Giant hot gas diffuse halo (100x100 kpc) Spectrum of hot gas: ~0.5 keV MEKAL; pressure 2x lower cosmic rays and B-fields
Conclusions: Radio lobes & hot gas halo likely due to galactic superwind, driven by cosmic rays
Structure in Clusters and Groups of Galaxies in the Chandra Era | X-raying the Mach cones of Virgo Cluster spiral galaxies | M. Ehle | Pag. 11 Observational results (4/4): The Mach Cones
NGC 4501 NGC 4388 NGC 4569
Assumption: all extra-planar X-ray emission is confined by Mach cones ⇒ can ‘fit’ cones: directions based on dynamical model; opening angles ‘adjusted’ -1 Mach cone opening angles ⇔ Mach number: α = sin (1/M) (M=vgal / cS)
Structure in Clusters and Groups of Galaxies in the Chandra Era | X-raying the Mach cones of Virgo Cluster spiral galaxies | M. Ehle | Pag. 12 What the Cones can tell us…
The case NGC 4569 (other galaxies: cf. paper): • Expectations:
vgal = 1500 km/s (estimated)
cs = 550-700 km/s (ICM, depending on adiabatic index) ⇒ M ~ 2.1-2.7 ⇒ α = 22-28 deg • Observations: α = 37.5 deg, adding projection (velocity vector) ⇒ true α = 30 deg (+/- 10)
Consistent but somewhat high…we can do better:
• ICM ionized & magnetized ⇒ not cs but magnetosonic velocity is important: 2 2 vms=sqrt (cs + va );
va=B/sqrt(4πnmp) Alfvén speed
• To reach α=30-32 deg (with vgal, cs, -4 -3 n=10 cm ) one needs va=300-600 km/s
⇒ B(cluster) ~1-3 µG (at location of NGC 4569), consistent with e.g. Ferrari et al. 2008
Structure in Clusters and Groups of Galaxies in the Chandra Era | X-raying the Mach cones of Virgo Cluster spiral galaxies | M. Ehle | Pag. 13 Conclusions
Summary: first time detection of Mach cones of a cluster spiral galaxy which moves supersonically in a cluster atmosphere (Mach number 2-3). Mach cone of NGC 4569 filled with hot gas from galactic outflow, detected in X- rays and radio continuum XMM-Newton data represent direct proof of the dynamical model predictions. Based on Mach cone opening angle it is possible to determine the galaxy velocity and to estimate the strength of the intracluster magnetic field. Based on the X-ray spectra it is possible to separate the different components of the hot gas (ISM, outflow, ICM) and to determine their densities and temperatures. Results are important for the understanding of the evolution of cluster spiral galaxies and clusters as a whole.
Thanks for your attention.
Structure in Clusters and Groups of Galaxies in the Chandra Era | X-raying the Mach cones of Virgo Cluster spiral galaxies | M. Ehle | Pag. 14